JP2001110618A - Method for manufacturing ferrite magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain changes in magnetic characteristics which is caused by fluctuation of oxygen partial pressure in a baking atmosphere, when a ferrite magnet having high residual magnetic flux density and high coercive force is manufactured. SOLUTION: This manufacturing method of a ferrite magnet is provided with a baking process, which obtains a sintered magnet by baking a molded object of a material powder. In a baking process, the oxygen partial pressure in an atmosphere is lower than that of the air. The sintered magnet contains Fe, an element A (A is at least one kind selected from among Sr, Ba, Ca and Pb), an element R (R is at least one kind selected from among rare earth elements (including Y) and Bi), element M (M is at least one kind selected from among Co, Mn, Ni and Zn), and element MB (MB is at least one kind selected from among B, Ti, V, Ge, Zr, Nb, Mo, Sn, Ta and W), and has a hexagonal system ferrite as the main phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a magnetoplumbite-type hexagonal ferrite magnet.

[0002]

2. Description of the Related Art Hexagonal magnetoplumbite (M-type) Sr ferrite or Ba ferrite is mainly used as an oxide permanent magnet material, and these are used as sintered magnets or bonded magnets. ing.

[0003] Of the magnet properties, particularly important are the residual magnetic flux density (Br) and the intrinsic coercive force (HcJ). Br
Is determined by the relative density and the degree of orientation of the magnet and the saturation magnetization (4πIs) determined by the crystal structure thereof, and is expressed by Br = 4πIs × degree of orientation × relative density. The 4πIs of M-type Sr ferrite and Ba ferrite is about 4.65 kG. The relative density and the degree of orientation are each limited to about 98% even in the case of the sintered magnet which can obtain the highest value. Therefore, the limit of Br of these magnets is about 4.46 kG, and it has been practically impossible to obtain high Br of 4.5 kG or more.

On the other hand, the present inventors have disclosed, for example,
Japanese Patent Application Laid-Open No. 1-154604 proposes a ferrite magnet having a high residual magnetic flux density and a high coercive force, which cannot be achieved by a conventional M-type ferrite magnet. This ferrite magnet is at least one element selected from Sr, Ba, Ca, and Pb, and always includes Sr and includes at least one element selected from rare earth elements (including Y) and Bi. When R is an element that always contains La and Co or Co and Zn is an element M, the total composition ratio of each metal element of A, R, Fe and M is represented by the total metal element amount. A: 1 to 13 atomic%, R: 0.05 to 10 atomic%, Fe: 80 to 95 atomic%, M: 0.1 to 5 atomic% It has.

Japanese Patent Application Laid-Open No. Hei 10-149910 discloses that (Sr _1-x R _x ) On · [(Fe _{1- y My} ) ₂ O ₃ ] (where R is La, Nd and Pr). At least one kind, and M is at least one kind of Mn, Co, Ni and Zn), wherein 0.05 ≦ x ≦ 0.5, {x / (2.2n)} ≦ y ≦ It has been proposed that {x / (1.8n)}, 5.70 ≦ n <6.00. In order to improve the saturation magnetization, the invention described in the publication discloses that an Fe ion corresponding to a magnetic moment oriented in the antiparallel direction is replaced with another element having a smaller magnetic moment than the Fe ion or a non-magnetic element ( The charge compensation is performed by substituting the Sr site with another element (the above R) in order to suppress the generation of a different phase while substituting with the above M).

[0006]

In the process of studying the optimum conditions for manufacturing a ferrite magnet disclosed in Japanese Patent Application Laid-Open No. H11-154604, the present inventors have found that the magnetic characteristics are greatly affected by the firing conditions. I found it to be received. Specifically, it was found that the coercive force was significantly reduced when the oxygen partial pressure in the firing atmosphere fluctuated, particularly when the oxygen partial pressure was lower than in air.

However, when a ferrite magnet is manufactured, in the firing step, oxygen absorption due to decomposition and combustion of a binder, a dispersant, and the like, oxygen absorption due to a change in the valence of a constituent element and a change in structure are caused. -The oxygen partial pressure in the firing atmosphere is constantly fluctuating due to release and the like. Since the width of the fluctuation varies greatly depending on various conditions, such as the composition of the object to be fired and the amount to be charged into the firing furnace, the type and amount of the additive,
It is difficult to control the oxygen partial pressure to be always constant. Therefore, it is difficult to stably realize the original high coercive force with a ferrite magnet having a composition whose characteristics are easily affected by changes in the oxygen partial pressure during firing.

In particular, in a continuous furnace which is effective for improving productivity in mass production, the fluctuation of the oxygen partial pressure is larger than in a batch furnace. Also, in furnaces that require low costs for firing, such as gas combustion furnaces that heat by utilizing the combustion of fuel, such as gas combustion furnaces, which consumes oxygen when burning fuel, the oxygen partial pressure in the furnace fluctuates drastically. I do. Therefore, when using continuous furnaces and combustion furnaces and combustion furnace type continuous furnaces,
In particular, a ferrite magnet that is less susceptible to fluctuations in oxygen partial pressure during firing is required.

The present invention has been made in view of such circumstances, and when manufacturing a ferrite magnet having a high residual magnetic flux density and a high coercive force, the magnetic characteristics due to the fluctuation of the oxygen partial pressure in the firing atmosphere are reduced. The purpose is to suppress fluctuations.

[0010]

This and other objects are achieved by the present invention which is defined below as (1) and (2). (1) There is a firing step of firing a compact of the raw material powder to obtain a sintered magnet, and in at least a part of the firing step, the oxygen partial pressure in the atmosphere is lower than the oxygen partial pressure in the air. The sintered magnet is composed of Fe, element A (A is Sr, B
a, at least one selected from Ca and Pb),
Element R (R is at least one selected from rare earth elements (including Y) and Bi), element M (M is Co, M
n, at least one) and the element M _B (M _B is selected from Ni and Zn, B, Ti, V, Ge , Zr, N
b, at least one selected from the group consisting of Mo, Sn, Ta and W), and has a hexagonal ferrite as a main phase. (2) When the contents of the element A, the element R, and the element M are converted into oxides and the contents thereof are determined, a formula IA _1-x R _x (Fe _{12- y My} ) _z O ₁₉ (in the above formula I, , 0.04≤x≤0.9, 0.04≤y≤0.5, 0.4≤x / y≤4, 0.7≤z≤1.2) and the element the content of M _B is the formula composite oxide 100 mol represented by I to 0.4 to 15
The method for producing a ferrite magnet according to the above (1), wherein a sintered magnet having a molar composition is produced.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Sintered Magnet A ferrite magnet produced according to the present invention has a hexagonal magnetoplumbite type (M type) ferrite as a main phase, Fe, an element A (A is Sr, Ba, Ca and Pb
Element R (R is at least one element selected from rare earth elements (including Y) and Bi), element M (M is Co, Mn, Ni and Zn
At least one) and the element M _B is selected from (M
_B is B, Ti, V, Ge, Zr, Nb, Mo, Sn,
At least one selected from Ta and W).

[0012] The present invention is characterized by the inclusion of the element M _B in the magnet. By containing the element M _B,
Even when firing is performed under an oxygen partial pressure lower than the oxygen partial pressure in the air, a decrease in coercive force can be significantly suppressed. That is, when the addition of the element M _B and fired at low oxygen partial pressure, compared with those fired without the addition and the same low oxygen partial pressure, coercive force becomes significantly higher, or the coercive force is equal to the coercive force Even if the improvement rate is low, the change in coercive force due to the change in oxygen partial pressure is small.

When the content in the magnet is determined by converting the element A, the element R, and the element M into oxides, respectively, the formula IA _1-x R _x (Fe _{12- y My} ) _z O ₁₉ (described above) 0.04 ≦ x ≦ 0.9, 0.04 ≦ y ≦ 0.5, 0.4 ≦ x / y ≦ 4, 0.7 ≦ z ≦ 1.2 in Formula I) Is preferred. Further, the content of the element M _B, compared composite oxide 100 mol of the formula I, preferably 0.4 to 15 moles, more preferably 1
10 to 10 mol. Further, the more preferable content of the element other than _{B in} the element MB is 2 to 7 mol. Effect of the present invention and M _B content is too low may be insufficient, M _B
If the content is too large, there arises a problem that sinterability deteriorates and saturation magnetization decreases.

When calculating the content by converting the metal element contained in the magnet into its general oxide, the content of Fe → Fe ₂ O ₃ , Sr → SrO, Ba → BaO, Ca → CaO , Pb → PbO, Rare earth element RE → RE ₂ O ₃ (where Pr is Pr
₆ O ₁₁ , Ce is CeO ₂ , Tb is Tb ₄ O ₇ ), Bi → Bi ₂ O ₃ , Co → CoO, Mn → MnO, Ni → NiO, Zn → ZnO.

Next, the reasons for limiting the composition ratio in the above formula I will be described.

In the above formula I, if x is too small, that is, if the amount of the element R is too small, the amount of the element M dissolved in the hexagonal ferrite cannot be increased, and the effect of improving the saturation magnetization and / or The effect of improving the sexual magnetic field becomes insufficient. If x is too large, the element R cannot be substituted and dissolved in the hexagonal ferrite.
Is generated and the saturation magnetization decreases. If y is too small, the effect of improving the saturation magnetization and / or the effect of improving the anisotropic magnetic field become insufficient. If y is too large, the element M cannot be substituted and solid-solved in the hexagonal ferrite. Further, even in a range where the element M can be substituted for a solid solution, the anisotropy constant (K ₁ ) and the anisotropic magnetic field (H _A ) greatly deteriorate. If z is too small, the nonmagnetic phase containing Sr and the element R increases, so that the saturation magnetization decreases. If z is too large, the α-Fe ₂ O ₃ phase or the element M
, The saturation magnetization decreases.

In the above formula I, even if x / y is too small,
Even if it is too large, the valence of element R and element M cannot be balanced.
As a result, a different phase such as W-type ferrite is easily generated. Former
Element M is a divalent ion and element R is a trivalent ion
In some cases, it is general to set x / y = 1 in terms of valence equilibrium
However, in the present invention, it is preferable that R is excessive.
No. Note that the reason why the allowable range is large in the region where x / y exceeds 1 is
Means that even if y is small, ³⁺→ Fe²⁺Valence by reduction of
This is because the balance can be obtained.

In the above formula I representing the composition, the number of atoms of oxygen (O) is 19, because M is all divalent, R is all trivalent, and x = y, z =
It shows the stoichiometric composition ratio of oxygen at the time of 1.
The number of oxygen atoms differs depending on the types of M and R and the values of x, y, and z. Further, for example, when the firing atmosphere is a reducing atmosphere, oxygen deficiency (vacancy) may occur. Further, Fe is usually trivalent in M-type ferrite, but this may change to divalent or the like. In addition, the valence of the element M such as Co may change, and the ratio of oxygen to the metal element changes accordingly. In this specification, the number of oxygen atoms is indicated as 19 regardless of the type of R and the values of x, y, and z. However, the actual number of oxygen atoms may be a value slightly deviated from this.

The magnet composition can be measured by a fluorescent X-ray quantitative analysis or the like. The presence of the main phase can be confirmed by X-ray diffraction, electron beam diffraction, or the like.

In order to increase the saturation magnetization and the coercive force of the magnet, it is preferable to use at least one of Sr and Ca as the element A, and it is particularly preferable to use Sr. The proportion of Sr + Ca in A is preferably at least 51 atomic%, more preferably at least 70 atomic%,
More preferably, it is 100 atomic%.

As the element R, preferably at least one kind of lanthanoid, more preferably at least one kind of light rare earth, further preferably at least one kind of La, Nd and Pr are used, and it is particularly preferable to always use La. The proportion of La occupied in R is preferably 40
It is at least 70 atomic%, more preferably at least 70 atomic%, and it is most preferable to use only La as R for improving the saturation magnetization. This is because, when comparing the solid solution limit amount to hexagonal M-type ferrite, La is the largest.
Therefore, if the ratio of La in R is too low, the amount of solid solution of R cannot be increased, and as a result, the amount of solid solution of element M cannot be increased, and the effect of improving magnetic properties is reduced. I will. When Bi is used in combination, the calcining temperature and the sintering temperature can be lowered, which is advantageous in production.

As the element M, at least Co and Z
It is preferable to use at least one kind of n, particularly Co.
The proportion of Co in M is preferably at least 10 atomic%, more preferably at least 20 atomic%. If the proportion of Co in M is too low, the coercive force is insufficiently improved.

The magnet may contain at least one of Na, K and Rb. These are respectively Na
When converted to ₂ O, K ₂ O and Rb ₂ O, the total of these contents is preferably 3% by weight or less of the whole magnet powder. If these contents are too large, the saturation magnetization will be low. When these elements expressed in M ^I, M ^I in ferrite is contained, for example, in the form of ^{_{Sr 1.3-2a R a M I a-}} 0.3 Fe 11.7 M 0.3 O 19. In this case, 0.3 <a ≦ 0.
It is preferably 5. When a is too large, in addition to the saturation magnetization becomes low, a problem that the element M ^I is thus a large amount of evaporation occurs during firing.

The atomic ratio R / M in the magnet is preferably from 0.7 to 1.5. When M is divalent, it is preferable that M = R in terms of valence equilibrium. However, by making R excessive relative to M, the effect of the present invention is enhanced.

In addition to the above elements, for example, Al, C
r, Ga, In, Li, Mg, Cu, Sb, As or the like may be contained as an oxide. These contents are
In terms of oxides of stoichiometric composition, aluminum oxide is 5% by weight or less, chromium oxide 5% by weight or less, gallium oxide 5% by weight or less, indium oxide 3% by weight or less, lithium oxide 1% by weight or less, magnesium oxide It is preferable that the content is 3% by weight or less, copper oxide 3% by weight or less, antimony oxide 3% by weight or less, and arsenic oxide 3% by weight or less.

Manufacturing Method Next, a method for manufacturing a magnet will be described.

The production method of the present invention has a firing step of firing a compact of the raw material powder to obtain a sintered magnet.

The method for producing the raw material powder is not particularly limited. For example, the raw material powder may be produced by a solid phase reaction by so-called calcination, or may be produced by a coprecipitation method or a hydrothermal synthesis method.
Hereinafter, a case in which the calcination step is provided will be mainly described.

First, the starting materials are mixed and then calcined to obtain a calcined body. The calcined body is pulverized by pulverization or pulverization to obtain the raw material powder. Then, after the raw material powder is formed, it is fired.

In the magnet having the above composition, even when the oxygen partial pressure in the atmosphere fluctuates in the firing step, the fluctuation of the magnetic properties, particularly the fluctuation of the coercive force, is small. In at least a part of the firing step, the present invention exhibits a remarkably high effect when the oxygen partial pressure in the firing atmosphere is 0.15 atm or less, particularly when it is 0.10 atm or less.
Therefore, the present invention is suitable for the case of using a gas continuous furnace in which the oxygen partial pressure in the furnace is low.

Next, preferable manufacturing conditions and the like will be described.

As a starting material, an oxide powder or a compound which becomes an oxide upon firing, for example, a powder of a carbonate, a hydroxide, a nitrate or the like is used. The average particle size of the starting material is not particularly limited, but is usually preferably about 0.1 to 2 μm. In particular, it is preferable to use fine powder for iron oxide, and specifically, the average particle size of primary particles is preferably 1 μm.
Hereafter, more preferably, those having a size of 0.5 μm or less are used.
In addition, as the starting material containing the element A, it is preferable to use a hydroxide or a carbonate because the stability at the time of stock is good.

The calcination may be usually performed in an oxidizing atmosphere such as air. The calcination conditions are not particularly limited, but usually,
The stabilization temperature is 1000-1350 ° C, and the stabilization time is 1 second
The time may be set to 10 hours, more preferably 1 second to 3 hours. The calcined body has a substantially magnetoplumbite-type ferrite structure, and the average particle size of its primary particles is preferably 2 μm or less, more preferably 1 μm or less, still more preferably 0.1 to 1 μm, and most preferably. 0.1-0.5
μm. The average particle size can be measured by a scanning electron microscope.

In the present invention, it is preferable to use SiO ₂ as a starting material for supplying Si. SiO ₂
It may be mixed with other starting materials before calcination, mixed after calcination, or the addition of SiO ₂ may be divided between before and after calcination. If at least SiO ₂ is added before firing, the effect of the addition of SiO ₂ is realized. However, in order to further improve the effect on fluctuations in firing conditions, it is preferable to add part or all of SiO ₂ after calcination.

The starting compounds other than SiO ₂ are also
It is not necessary to mix all of them before calcination, and it may be configured to add a part or all of each compound after calcination.

It is preferable to use a wet molding method for molding the raw material powder. In wet molding, it is preferable to use a molding slurry containing a raw material powder, water as a dispersion medium, and a dispersant. In order to further enhance the effect of the dispersant, it is preferable to provide a wet pulverization step before the wet molding step. When the calcined body powder is used as the raw material powder, the calcined body powder is generally composed of granules. Therefore, in order to roughly pulverize or pulverize the calcined body powder, a dry coarse pulverization step is performed before the wet pulverization step. Is preferably provided. When the raw material powder is manufactured by a coprecipitation method, a hydrothermal synthesis method, or the like, usually, a dry coarse grinding step is not provided, and a wet grinding step is not essential. It is preferable to provide a pulverizing step. The case where the calcined particles are used as a raw material powder and a dry coarse pulverizing step and a wet pulverizing step are provided will be described below.

In the dry coarse pulverization step, pulverization is usually performed until the BET specific surface area becomes about 2 to 10 times. After pulverization, the average particle size is preferably about 0.1 to 1 μm,
The specific surface area is preferably about 4 to 10 m ² / g. The pulverizing means is not particularly limited. For example, a dry vibrating mill, a dry attritor (medium stirring type mill), a dry ball mill and the like can be used, and it is particularly preferable to use a dry vibrating mill. The pulverization time may be appropriately determined according to the pulverization means. In addition, when adding some starting materials after calcination, it is preferable to add in this dry coarse pulverization process. For example, it is preferable that at least a part of each of SiO ₂ and CaCO ₃ which becomes CaO by firing is added in the dry coarse pulverization step.

Dry coarse pulverization also has the effect of introducing crystal strain into the calcined particles to reduce the coercive force HcB. Due to the decrease in coercive force, aggregation of particles is suppressed, and dispersibility is improved. In addition, the degree of orientation is also improved by softening. The softened particles return to their original hard magnetism in a subsequent sintering step.

After the dry coarse pulverization, a pulverization slurry containing the pulverized particles and water is prepared, and wet pulverization is performed using the slurry. The content of the raw material powder in the slurry for pulverization is 10 to
It is preferably about 70% by weight. The grinding means used for wet grinding is not particularly limited, but is usually a ball mill,
It is preferable to use an attritor, a vibration mill or the like. The pulverization time may be appropriately determined according to the pulverization means.

After the wet pulverization, the pulverizing slurry is concentrated to prepare a molding slurry. Concentration may be performed by centrifugation or the like. The content of the raw material powder in the molding slurry is preferably about 60 to 90% by weight.

In the wet molding step, molding in a magnetic field is performed using a molding slurry. Molding pressure is 0.1 ~ 0.5t / cm ²
And the applied magnetic field may be about 5 to 15 kOe.

When a non-aqueous dispersion medium is used in the molding slurry, a high degree of orientation can be obtained. However, in order to reduce the load on the environment, it is preferable to use an aqueous dispersion medium. In order to compensate for the decrease in the degree of orientation due to the use of the aqueous dispersion medium, it is preferable that a dispersant is present in the molding slurry. The dispersant used in this case is an organic compound having a hydroxyl group and a carboxyl group, a neutralized salt thereof, or its lactone, an organic compound having a hydroxymethylcarbonyl group, or an acid. It is preferable that the compound is an organic compound having a dissociable enol-type hydroxyl group or a neutralized salt thereof.

When a non-aqueous dispersion medium is used,
For example, as described in Japanese Patent No. 2838632, a surfactant such as oleic acid is added to an organic solvent such as toluene or xylene to form a dispersion medium. By using such a dispersion medium, it is possible to obtain a high degree of magnetic orientation of about 98% at the maximum even when ferrite particles having a submicron size that are difficult to disperse are used.

Each of the above organic compounds has 3 to 20 carbon atoms,
It is preferably 4 to 12, and a hydroxyl group is bonded to 50% or more of carbon atoms other than the carbon atom double-bonded to the oxygen atom. When the number of carbon atoms is 2 or less, the effect of improving the degree of orientation becomes insufficient. Even if the number of carbon atoms is 3 or more, the effect is still insufficient if the bonding ratio of the hydroxyl group to carbon atoms other than the carbon atom double-bonded to the oxygen atom is less than 50%. The bonding ratio of the hydroxyl group is limited for the above-mentioned organic compound, and is not limited for the dispersant itself. For example, when a lactone of an organic compound having a hydroxyl group and a carboxyl group (hydroxycarboxylic acid) is used as a dispersant,
The limitation on the bonding ratio of hydroxyl groups applies to hydroxycarboxylic acids themselves, not lactones.

The basic skeleton of the above organic compound may be a chain or a cyclic, and may be saturated or contain an unsaturated bond.

As the dispersant, specifically, a hydroxycarboxylic acid or a neutralized salt thereof or a lactone thereof is preferable. In particular, gluconic acid (C = 6; OH = 5; COOH
= 1) or a neutralized salt thereof or a lactone thereof, lactobionic acid (C = 12; OH = 8; COOH = 1), tartaric acid (C = 4; OH = 2; COOH = 2) or a neutralized salt thereof, glucoheptone Acid γ-lactone (C = 7; OH
= 5) is preferred. Among these, gluconic acid or its neutralized salt or its lactone is preferable because it has a high effect of improving the degree of orientation and is inexpensive.

As the organic compound having a hydroxymethylcarbonyl group, sorbose is preferred.

As the organic compound having an enol type hydroxyl group which can be dissociated as an acid, ascorbic acid is preferable.

In the present invention, citric acid or a neutralized salt thereof can also be used as a dispersant. Citric acid has a hydroxyl group and a carboxyl group, but does not satisfy the condition that a hydroxyl group is bonded to 50% or more of carbon atoms other than a carbon atom double-bonded to an oxygen atom. However, the effect of improving the degree of orientation is recognized.

For some of the preferred dispersants described above,
The structure is shown below.

[0051]

Embedded image

The degree of orientation by magnetic field orientation is determined by the pH of the slurry.
Affected by Specifically, if the pH is too low, the degree of orientation decreases, which affects the residual magnetic flux density after sintering. When a compound exhibiting an acid property in an aqueous solution, such as hydroxycarboxylic acid, is used as the dispersant, the pH of the slurry becomes low. Therefore,
For example, it is preferable to adjust the pH of the slurry by adding a basic compound together with the dispersant. As the basic compound, ammonia and sodium hydroxide are preferable. Ammonia may be added as aqueous ammonia. In addition, by using the sodium salt of hydroxycarboxylic acid, the pH can be prevented from lowering.

As a raw material, SiO_TwoAnd CaCO_ThreeUsing
If used, hydroxycarboxylic acid or its lactide
Tons are used mainly when preparing slurry for molding.
SiO with rally supernatant_TwoAnd CaCO_ThreeLeaked
And the desired performance, such as a decrease in HcJ, cannot be obtained.
Become. In addition, the pH is adjusted by adding the above basic compound.
Is increased, the SiO_TwoAnd CaCO_ThreeOutflow
Will be more. In contrast, hydroxycarboxylic acids
If a calcium salt is used as a dispersant, SiO _Twoand
CaCO_ThreeOutflow is suppressed. However, the above basification
Compound was added or sodium salt was used as dispersant
In the case of_TwoAnd CaCO_ThreeTo target composition
On the other hand, if it is added in excess, SiO_TwoQuantity and Ca
Insufficiency of the amount of O can be prevented. In addition, ascorbic acid
When used, SiO_TwoAnd CaCO_ThreeOutflow
Almost not.

For the above reasons, the pH of the slurry is preferably 7 or more, more preferably 8 to 11.

The kind of the neutralizing salt used as the dispersing agent is not particularly limited, and may be any of a calcium salt and a sodium salt. For the above-mentioned reason, the calcium salt is preferably used. When a sodium salt is used as the dispersant or when ammonia water is added, there is a problem that, in addition to the outflow of subcomponents, cracks are easily generated in the formed body and the sintered body.

Incidentally, two or more dispersants may be used in combination.

The amount of the dispersant added is preferably 0.05 to 3.0% by weight, more preferably 0.10% by weight, based on the raw material powder.
~ 2.0% by weight. If the amount of the dispersant is too small, the degree of orientation will not be sufficiently improved. On the other hand, if the amount of the dispersing agent is too large, cracks are likely to occur in the molded body and the sintered body.

When the dispersant is one that can be ionized in an aqueous solution, for example, an acid or a metal salt, the amount of the dispersant to be added is an ion equivalent. That is, the amount of addition is determined in terms of organic components excluding hydrogen ions and metal ions.
When the dispersant is a hydrate, the amount of addition is determined excluding water of crystallization. For example, when the dispersant is calcium gluconate monohydrate, the amount to be added is calculated in terms of gluconate ions.

When the dispersant is made of lactone or contains lactone, the amount of addition is determined in terms of hydroxycarboxylic acid ions, assuming that all of the lactone is opened to form hydroxycarboxylic acid.

The time of addition of the dispersant is not particularly limited, and may be added during dry coarse pulverization, may be added during preparation of a slurry for wet pulverization, and may be partially added during dry coarse pulverization. And the remainder may be added during wet grinding. Alternatively, it may be added by stirring after wet pulverization. In any case, since the dispersant is present in the molding slurry, the effect of the addition of the dispersant is realized. However, it is better to add at the time of grinding, especially at the time of dry coarse grinding,
The effect of improving the degree of orientation increases. In a vibration mill or the like used for dry coarse pulverization, larger energy is given to the particles than in a ball mill or the like used for wet pulverization, and the temperature of the particles increases, so that the chemical reaction is likely to proceed. Therefore, if a dispersant is added at the time of dry coarse pulverization, the amount of the dispersant adsorbed on the particle surface increases, and as a result, a higher degree of orientation is considered to be obtained. Actually, when the residual amount of the dispersing agent in the molding slurry (which is considered to be almost equal to the adsorption amount) is measured, the amount of the dispersing agent added during the dry coarse grinding is larger than that when the dispersing agent is added during the wet grinding. The ratio of the residual amount to is increased. In addition, when the dispersant is added in a plurality of times,
What is necessary is just to set the addition amount of each time so that the total addition amount may be in the preferable range described above.

After the wet molding, the molded body is dried,
Preferably 100 to 500 in air or nitrogen
By applying heat treatment at a temperature of ° C., the added dispersant is sufficiently decomposed and removed. Drying and the heat treatment may be performed continuously, but if the molded body is rapidly heated without being sufficiently dried, cracks occur in the molded body,
It is preferable that the temperature is slowly increased from room temperature to about 100 ° C., and that drying is sufficiently performed in this temperature range. After the heat treatment, firing is performed to obtain a sintered ferrite magnet.
The stable temperature during firing is preferably 1150 to 1250.
° C, more preferably 1160 to 1240 ° C, and the time for maintaining the temperature at a stable temperature is preferably 0.5 to 3 hours. As described above, for example, in a continuous furnace, a stabilization process may not be provided.

The average crystal grain size of the magnet is preferably 2 μm
Hereinafter, it is more preferably 1 μm or less, and still more preferably 0.5 to 1.0 μm. In the present invention, a sufficiently high coercive force can be obtained even if the average crystal grain size exceeds 1 μm. The crystal grain size can be measured by a scanning electron microscope. The specific resistance is usually a 10 ⁰ [Omega] m or more.

The compact was crushed using a crusher or the like, and the average particle size was 100 to 700 μm by sieving or the like.
The magnets may be obtained by classifying the granules so as to have a particle size of about m to obtain magnetic-field-oriented granules, subjecting them to dry magnetic field molding, and sintering them.

In the ferrite magnet produced according to the present invention, a high coercive force and a high saturation magnetization are realized by containing the element R and the element M. Therefore, if it has the same shape as a conventional ferrite magnet that does not contain these elements, the generated magnetic flux density can be increased, and when applied to a motor, high torque can be realized, and it can be applied to speakers and headphones. In this case, the magnetic circuit can be strengthened to obtain sound quality with good linearity, thereby contributing to higher performance of applied products. If the same function as that of a conventional ferrite magnet is sufficient, the size (thickness) of the magnet can be reduced (thinned), which contributes to reduction in size and weight (thinness). Further, even in a motor in which a field magnet is conventionally a winding type electromagnet, this can be replaced with a ferrite magnet, which contributes to weight reduction, shortening of a production process, and cost reduction. Further, the coercive force (Hc
J) Excellent temperature characteristics make it possible to use it even in low-temperature environments where there was a risk of low-temperature demagnetization (permanent demagnetization) of ferrite magnets, especially for products used in cold regions and in the sky. Properties can be significantly increased. Further, in the present invention, even if the firing conditions are unstable, ferrite magnets having the above-described excellent characteristics can be stably mass-produced. Large contribution to

The magnet manufactured according to the present invention is processed into a predetermined shape and used for a wide range of applications as described below.

For example, for fuel pump, power window, ABS, fan, wiper, power steering, active suspension, starter,
Automotive motors for door locks, electric mirrors, etc .; FD
For D spindle, VTR capstan, VTR rotary head, VTR reel, VTR loading, VT
For R camera capstan, VTR camera rotating head,
Motors for OA and AV equipment such as VTR camera zoom, VTR camera focus, boombox capstan, CD, LD, MD spindle, CD, LD, MD loading, CD, LD optical pickup, etc .; air conditioner compressor Motors for household appliances such as refrigerator compressor, electric tool drive, electric fan, microwave oven fan, microwave oven plate rotation, mixer drive, dryer fan drive, shaver drive, electric toothbrush, etc .;
Motors for FA equipment such as robot axes, joint drive, robot main drive, machine tool table drive, machine tool belt drive, etc .; motor generators, magnets for speakers and headphones, magnetron tubes, magnetic field generation for MRI It can be used for devices, CD-ROM clampers, distributor sensors, ABS sensors, fuel and oil level sensors, magnet latches, and the like.

[0067]

EXAMPLE 1 SrCO ₃ , La ₂ O ₃ , CoO _x , Fe ₂ O ₃ , SiO ₂ and CaCO ₃ were blended, mixed and pulverized by a wet attritor for 5 hours, and dried and adjusted. Granulated to give granules. The granules were calcined in air at 1250 ° C. for 3 hours to obtain a calcined material.

[0068] This calcined material was added SiO ₂ and CaCO _3, and coarsely pulverized by a dry vibration mill. Note that [calcined prior to the addition amount: amount to calcined material] is the SiO ₂ 1: 2 and then, was the CaCO ₃ 3:25.

[0069] To the resulting roughly pulverized material was added M _B oxide. The addition amount of M _B oxide in the final composition (the magnet composition) to [Elemental A + element R] 100 mol elemental M _B was set to the moles indicated in Table 1. Next, after performing wet pulverization with a ball mill for 40 hours, the slurry was dehydrated and concentrated to a concentration of about 75% to obtain a molding slurry.

[0070] For comparison, also produced molding slurry containing no M _B oxide.

Next, the molding slurry was compression-molded while dewatering to obtain a molded body having a diameter of 30 mm and a height of 18 mm. At the time of compression molding, a magnetic field of about 10 kOe was applied in the compression direction. The molding pressure was 0.4 t / cm ² .

Next, the compact was fired to obtain a sintered magnet. The firing is performed in a mixed gas atmosphere (1 atm) of oxygen gas and nitrogen gas using a tubular furnace, and by controlling the flow rates of both gases, the oxygen partial pressure pO ₂ in the firing atmosphere is reduced to 0.2.
Atmospheric pressure or 0.02 atm was controlled. The heating rate and the cooling rate during firing were 5 ° C./min, and the firing temperature was 11 ° C.
95 ° C, and the time to maintain the firing temperature (stabilization time) is 1
Time.

[0073] The composition of the sintered magnet was not added element M _B was examined by X-ray fluorescence analysis, Fe ₂ O _3: 80.999 mol%, MnO: 0.608 mole%, SrO: 10.858 mol%, BaO: 0.122 mol%, SiO _2: 1.209 mol%, CaO: 1.978 mol%, ZnO: 0.007 mol%, La ₂ O _3: 1.338 mol%, CoO: 2 .722 mol%, Al ₂ O _3: 0.076 mol%, Cr ₂ O _3: 0.081 mol%, CuO: was 0.002 mol%.

After processing the upper and lower surfaces of these sintered magnets,
The coercive force HcJ and the residual magnetic flux density Br were measured. pO ₂
= HcJ _0.02 and Br _0.02 for the coercive force and residual magnetic flux density of the magnet fired at 0.02 atm, respectively, and pO ₂ =
The coercive force and residual magnetic flux density of the sintered magnets with 0.2 atm and HcJ _0.2 and Br _{0.2, respectively, △ HcJ = HcJ 0.02 -HcJ 0.2} , the △ Br = determined by Br _0.02 -Br _0.2 △ HcJ and △ Br , Are shown in Table 1. Further, HcJ _0.02 and Br _{0. 02} also shown in Table 1.

[0075]

[Table 1]

In Table 1, as ΔHcJ is closer to 0, the effect of the decrease in oxygen partial pressure is less.
If the value is positive, the characteristics improve due to the decrease in the oxygen partial pressure, and ΔHcJ
Is negative, it means that the characteristics are degraded due to a decrease in the oxygen partial pressure. The magnet was not added element M _B, △ HcJ is that a large negative value, it can be seen that the magnetic properties are greatly deteriorated by the oxygen partial pressure decrease during firing. In contrast, the element M
_In the magnet to which _B is added, the absolute value of ΔHcJ is small,
In some cases, J is a positive value. From this result, the effect of the element M _B added is evident.

By the way, when firing under a low oxygen partial pressure,
Generally, HcJ decreases, but Br increases. Therefore, △
Br is a positive value in each magnet. According to the study of the present inventors, if the magnets have substantially the same basic composition, 3B
It has been empirically known that r + HcJ (unit of Br: G, unit of HcJ: Oe) is almost constant. Therefore, based on Table 1, the difference of 3Br + HcJ due to the change in pO ₂ ｛△
By comparing｝ represented by (3Br + HcJ), it is possible to estimate a decrease in the potential of the magnet characteristics.
Doing comparison with and without the element M _B added from the viewpoint,
In the magnet not added, △ (3Br + HcJ) was −81.
In contrast to the large negative value of 9, the added magnet
Even the one with the largest drop is as small as -545 and +264
Some are That is, in some cases, the firing at a low oxygen partial pressure improves the potential of the magnet properties. From these results, the reduction in magnetic characteristics potential due to oxygen partial pressure drop during firing is considered to suppress the element M _B.

[0078] In the magnet was not added element M _B, when the average crystal grain size of the pO ₂ = 0.2 atm 0.8μ
m, pO whereas a which was 0.9μm when ₂ = 0.02 atm, the magnet Nb to 4.3 mol per mol of the element M _B, when the average crystal grain size of the pO ₂ = 0.2 atm Also pO ₂ =
It was 0.7 μm even at 0.02 atm. Scanning electron micrographs of the cross sections of these magnets are shown in FIGS. Figure 1 is a magnet added element M _B, (A)
Is the case where pO ₂ = 0.2 atm, and (B) is p
This is the case where O ₂ = 0.02 atm. Also, FIG. 2 is a magnet not added element M _B, (A) those in the case of a pO ₂ = 0.2 atm, (B), the pO ₂
= 0.02 atm. In these photographs, the direction of the c-axis is displayed. From these photos,
It can be seen that the growth of crystal grains and the plate formation of the crystal grains accompanying the firing under a low oxygen partial pressure were suppressed by the addition of Nb.
Even a magnet added with the element M _B other than Nb, it was confirmed that similarly grain growth and grain plate reduction is suppressed.

[0079]Example 2 Fe / Sr = 11.8 / 0.8 = 14.75 (atomic ratio)
SrCO _ThreeAnd Fe_TwoO_ThreeWeighed and wet
After mixing and grinding for 5 hours with a triter, dry
And sized to obtain granules. In the air, the granules
Calcination was performed at 1200 ° C. for 3 hours to obtain a calcined material.

The calcined material was added with La_Two(CO_Three)_Three・ 8H
_TwoO, CoO_x, SiO_TwoAnd CaCO _ThreeAnd add
In addition, 0.8 to the total of these additives and the calcined material
Weight percent calcium gluconate was added. In addition,
Element M_BB as an oxide of_TwoO_ThreeWas added. B_TwoO_ThreeAddition of
The amount is 100 mol of [element A + element R] in the final composition.
For element M_BIs set to be the number of moles shown in Table 2.
Was. Next, pulverization by a dry vibration mill was performed.

Next, after performing wet pulverization with a ball mill for 40 hours, the mixture was dehydrated and concentrated to a concentration of about 78% to obtain a molding slurry.

Using this slurry, molding was performed under the same conditions as in Example 1, and firing was performed under the same conditions as in Example 1 except that the firing temperature was set to 1220 ° C. to obtain a sintered magnet. .

[0083] The composition of the sintered magnet was not added element M _B was examined by X-ray fluorescence analysis, Fe ₂ O _3: 80.866 mol%, MnO: 0.603 mole%, SrO: 10.327 mol%, BaO: 0.121 mol%, SiO _2: 1.235 mol%, CaO: 2.378 mol%, ZnO: 0.005 mol%, La ₂ O _3: 1.599 mol%, CoO: 2 .614 mol%, Al ₂ O _3: 0.094 mol%, Cr ₂ O _3: was 0.158 mol%.

For these sintered magnets, the same measurement as in Example 1 was performed. Table 2 shows the results.

[0085]

[Table 2]

Table 2 shows that the addition of B suppresses the decrease in HcJ during firing under a low oxygen partial pressure. Further, when △ (3Br + HcJ) was obtained, it was -1010 for the magnet without B added, whereas, when B was added, the magnet with the largest decrease was only -470.

[0087]

According to the present invention, when a ferrite magnet having a high residual magnetic flux density and a high coercive force can be obtained by adding the element R and the element M, the element M _B
, The fluctuation of the magnetic properties due to the fluctuation of the oxygen partial pressure in the firing atmosphere can be remarkably suppressed.

[Brief description of the drawings]

1 (A) and 1 (B) are each a drawing substitute photograph showing a grain structure, and are scanning electron microscope photographs of a cross section of a ferrite magnet.

FIGS. 2 (A) and 2 (B) are each a drawing substitute photograph showing a particle structure, and are scanning electron microscope photographs of a cross section of a ferrite magnet.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4G018 AA02 AA08 AA09 AA10 AA11 AA12 AA15 AA16 AA17 AA18 AA19 AA21 AA22 AA23 AA25 AA27 AA32 AA33 AA34 AA37 AB04 AC02 AC14 AC16 5E040 AB04 AB09 BD01 CA01B

Claims (2)

[Claims] 1. A firing step of firing a compact of a raw material powder to obtain a sintered magnet, and in at least a part of the firing step, the oxygen partial pressure in the atmosphere is lower than the oxygen partial pressure in the air. The sintered magnet is composed of Fe, element A (A is Sr, Ba, C
a and Pb), an element R
(R is at least one selected from rare earth elements (including Y) and Bi), element M (M is Co, Mn, N
at least one) and the element M _B (M _B from i and Zn is selected, B, Ti, V, Ge , Zr, Nb, M
at least one selected from o, Sn, Ta and W
A method for producing a ferrite magnet, comprising: a seed) and having hexagonal ferrite as a main phase. 2. When the contents of the element A, the element R and the element M are converted into oxides and the contents thereof are determined, the formula IA _1-x R _x (Fe _{12- y My} ) _z O ₁₉ (the above formula In I, 0.04 ≦ x ≦ 0.9, 0.04 ≦ y ≦ 0.5, 0.4 ≦ x / y ≦ 4, 0.7 ≦ z ≦ 1.2) are satisfied, and , the content of the element M _B a composite oxide 100 mol of the formula I to 0.4 to 15
The method for producing a ferrite magnet according to claim 1, wherein a sintered magnet having a molar composition is produced.